1. Technical Field
The present invention relates to a liquid developer collecting system that includes a plurality of photosensitive bodies, a plurality of developing devices that develop electrostatic latent images formed on the photosensitive bodies by using liquid developer containing a non-volatile solvent as a carrier, and a transfer body that sequentially transfers the toner images developed by transfer units corresponding to the plural photosensitive bodies and stacks the transferred toner images to reuse liquid developer collected from the photosensitive bodies after transfer, and also relates to an image forming apparatus including the liquid developer collecting system.
2. Related Art
Various types of wet-type image forming apparatus that develop latent images using high-viscosity liquid developer to visualize electrostatic latent images have been proposed. The liquid developer used in a typical wet-type image forming apparatus contains toner having solid components and dispersed in a liquid solvent. The liquid developer used by the wet-type image forming apparatus contains solid constituents (toner particles) suspended in an electrically insulating organic solvent (carrier) such as silicon oil, mineral oil, and edible oil. The toner particles are extremely fine particles having particle diameters of about 1 μm. By using such fine toner particles, the wet-type image forming apparatus can provide images having a higher quality than that of images produced by a dry-type image forming apparatus, which uses powder toner particles having particle diameters of about 7 μm.
According to this type of image forming apparatus using liquid developer, a method has been proposed that develops an electrostatic latent image on a photosensitive body with liquid developer by using a developing device, transfers a toner image on the photosensitive body to a transfer body, and collects and reuses carrier-rich liquid developer by using a cleaner that contacts the photosensitive body after transfer.
The carrier-rich liquid developer is fed to a concentration control unit by using a pump or the like. The concentration control unit also receives liquid developer collected from the developing device. Then, the concentration control unit mixes a high-concentration liquid toner that has been supplied thereto and diluted liquid developer thus collected to adjust the concentration to a target solid concentration. The liquid developer adjusted to the target solid concentration is fed to the developing device for reuse (for example, see JP-A-2002-6637).
According to the method described above, however, adjustment to the target concentration needs to be performed for the carrier-rich liquid developer collected from the photosensitive body by the cleaner as well as the liquid developer collected from the developing device by a concentration control device before reuse. In the case of a color image forming apparatus, a concentration control device for collected liquid developer is provided for each color to prevent color mixture. For meeting the demand for size reduction of image forming apparatus, the capacity of each concentration control device needs to be small.
In order to adjust the concentration of the collected carrier-rich liquid developer to the target concentration using a small-capacity concentration control device, a new toner having a high concentration is supplied to the concentration control device from a toner tank. The concentration of the new toner is about 35%. Thus, when a solid concentration of the collected entire liquid developer is 17% under the condition of a target concentration set at 20%, a predetermined amount of the new toner having the concentration of 35% needs to be supplied by the concentration control device to adjust to the target concentration. In this case, the concentration cannot be efficiently adjusted when the concentration control device does not have sufficient vacant capacity.